NUTRIENT-UPTAKE BY FIELD-GROWN BROCCOLI AND NET NUTRIENT MOBILIZATION DURING INFLORESCENCE DEVELOPMENT

The growth pattern and removal of nutrients by broccoli (Brassica oleracea var italica cv. Emperor) plants were determined for a 44-day period following the transplantation of four-week-old seedlings to the field. Characteristics of xylem (root bleeding sap) and phloem (collected from stem incisions of an attached inflorescence) saps were similar to those reported previously for glasshouse-grown plants. The relative xylem sap composition was not markedly changed throughout the growing season. Only N and Zn showed net mobilization (24-31%) from the vegetative parts of the shoot (residual shoot), as estimated from declines in tissue concentrations during inflorescence development. Under conditions of adequate fertility broccoli plants removed 15.3 g N, 2.1 g P, 17.3 g K, 12.0 g Ca, 1.1 g Mg, 18.9 mg Mn, 10.8 mg Zn and 1.6 mg Cu m-2, and had a harvestable dry matter yield of 67 g m-2.